This program investigated the use of diamond heat spreaders and microencapsulated phase-change-material (microPCM) enhanced coolants to serve electronic systems with demanding size, weight and power requirements. Electrically-insulating and-conducting diamond films were deposited on a substrate and on a pulse power thyristor device. Both were placed onto a cold-plate heat exchanger and connected to an instrumented closed-loop experimental testbed. Experiments measured the enhanced performance of the diamond-coated heat spreaders and the thyristor compared to uncoated substrates and thyristors. Diamond films were also deposited onto GaAs substrates and repeatedly thermally cycled from-50° C to +150° C. The resistivity of the electrically-conducting diamond film heat spreader was measured as < 1 ohm-cm. The diamond film heat spreader reduced the surface temperature of the pulse power thyristor by 45° C (35%), reduced the interface temperature of the thyristor by 9°C (21%), and lowered its thermal resistance by 44. 5%. MicroPCM/PAO-enhanced coolants significantly increased heat transport and isothermal performance and required lower coolant flow rates. For the same flow rate as conventional ethylene/glycol or PAO coolants, microPCM coolants lowered electronic board temperatures 10-46%. Under constant power conditions, microPCM coolants also reduced flow rates by 50-70%. Overall, diamond film combined with the two-component microPCM-enhanced coolants were found to be very useful in increasing a system’s effective thermal performance.